A shadow in the brainstem, an imaging finding and description, is commonly seen on CT.There are several possibilities for the presence of a low-density shadow in the brainstem:1. Brainstem infarction, the most common cause. Often there are obvious clinical symptoms, there can be limb paralysis, medullary paralysis, and in severe cases, high fever, coma, and convulsions.2. Brainstem artifacts, which are also common. Often there are no clinical symptoms, review of the cranial magnetic resonance, did not see any abnormal lesions in the brainstem, mainly caused by CT machine artifacts. 3, brainstem inflammation. More serious inflammation of the brainstem, can appear on the CT low density shadow, magnetic resonance examination can help to confirm. Hormone shock or gammaglobulin shock therapy is needed.4. Brain stem tumor. It can be a glioma or a tumor of other origin, such as cavernous hemangioma or metastatic tumor. This kind of general prognosis is not good, because the brainstem is a surgical restricted area, and can not be targeted for surgical resection.